DV Questions & Answers

Digital video is arguably the most exciting development in videography in the last decade, and this holiday season DV camcorders are on everyone's wish list. We all know that DV looks better, but some of our readers want more details on why it looks better. In this Q&A session, we're going to answer some of your questions about the technology behind the tiny-but-powerful digital formats and answer a few other questions to help you gain a better understanding of the capability and promise of this innovative video format.

Q. What's the difference between Mini DV and just DV?

A. DV is a recording and playback standard for digital video, regardless of the format. Mini DV is a tape format that's intended for consumer camcorders.
The full-size DV tapes, which can hold up to 4 1/2-hours of digital video and audio, are used primarily by broadcast professionals. Interestingly, you don't need special adapters to play Mini DV tapes in full-size DV VCRs since the two tape formats are compatible (see comparison in Figure 1).

DV Compression

Q. Since there is so much compression in DV, doesn't that cause a considerable loss of video quality? And aren't those tiny tracks recorded on that little tape going to have far too many problems with dropouts?

A. As far as the absolute quality of DV, that's something you'll have to judge for yourself. It's far better than any previous consumer video format and has found wide acceptance in the professional video community as well. The image quality speaks for itself.
As for the potential for dropouts causing problems, designers of the DV format did not ignore this issue. Manufacturers store additional information on the tape that corrects errors and verifies data that is read on the tape. If both data and the codes needed to recover it accurately are lost, DV provides methods for generating "best guess" information based on surrounding frames. Figure 2 shows how DV corrects errors, but in practice it seems that error correction and interpolation are rarely needed. Generally speaking, dropouts and data loss are extremely rare.

Longevity

Q. Our videos are a treasure and I'm concerned about the long-term stability of magnetic tape. How well is DV suited for storage?

A. Whether digital or analog, any recording made on magnetic tape is subject to degradation over time. Wear of the tape, dust, damage and print-through are always a threat. Fortunately, digital recordings are much more immune to the effects of all these problems. Analog recordings attempt to track the recorded signal directly, and any change in the recorded signal results in a corresponding loss of information. Digital systems aren't so touchy. DV records information as ones and zeros and small changes in the value written to the tape have no effect on the data that will be read from the tape [See Error Correction Sidebar for clarification on why this is so].
This fundamental digital advantage, combined with the error correction and interpolation discussed above, makes DV the most reliable form of video recording ever placed in the hands of the consumer. However, like all other recordings on magnetic tape, they are subject to long term degradation since nothing lasts forever.

Apples and Apples<…